Breast cancer genetic risk factors discovered

A mammogram of a woman's breast. New research take the total number of gene regions linked to the risk of breast cancer to 18. Photograph: Martin Godwin

Scientists came a step closer today to identifying women more likely to develop breast cancer after the discovery of five genetic variants that increase the risk of the disease.

The study conducted by the Institute of Cancer Research (ICR) found that women who had the variants were 16% more likely to develop the cancer. Comparing the genetic codes of more than 16,500 women with breast cancer and a family history of the disease with about 12,000 women without either, it identified areas of DNA known to influence the risk of cancer.

The ICR research – which was funded by Cancer Research UK and the Wellcome Trust, and was published in the journal Nature Genetics – brings the total number of common, "low-risk" DNA areas associated with breast cancer to 18.

Dr Helen George, head of science information at Cancer Research UK, said: "This is by far the largest study of its kind to explore the common genetic variations that contribute to breast cancer risk. This research takes us a step closer to developing a powerful genetic test for the disease. Such a test could help doctors identify women who have an increased risk so that they can make informed decisions about how to take steps to reduce their chance of developing the disease."

One of the newly discovered DNA sites contains CDK2NA, a gene which regulates cell division and is altered in many tumours. It has also been linked to an increased risk of developing melanoma skin cancer.

But while the findings pave the way for more reliable susceptibility tests, scientists have yet to discover which genes are causing the increased risk.

Professor Nazneen Rahman, from the ICR, said: "Our results now take the total number of gene regions linked to the risk of breast cancer to 18, but we still don't know which genes are causing this increased risk. Identifying the underlying genes and mechanisms behind breast cancer development is essential to increasing our understanding of the disease and ultimately finding new treatments."

Breast cancer is the most common cancer in women in the UK, with more than 45,500 new diagnoses a year. Around 300 men also develop the disease each year. While lifestyle influences the risk, inherited genetic factors also play a significant part.

The majority of the inherited risk is thought to be caused by a combination of common genetic factors, such as the variants, which each feed in a small amount of risk.

Most of the new variants appear to be associated with hormone-sensitive breast cancer – the most common form of the disease – which is stimulated by oestrogen.